Quantitative determination of disodium edetate in ophthalmic and contact lens care solutions by reversed-phase high-performance liquid chromatography.

A specific and sensitive HPLC method has been developed for the quantitative determination of disodium edetate (1) in a variety of ophthalmic and contact lens care solutions. Using this method, a common contaminant, nitrilotriacetic acid (2), is easily separated from 1. Sample preparation involves a single dilution step prior to mixing with an aqueous cupric nitrate solution to form a copper:EDTA complex for analysis. An aliquot of the resulting mixture is analyzed by HPLC using either a 10-microns styrene divinyl benzene column or, for separations requiring greater selectivity and resolution because of interfering components in the sample matrix, a 5-microns octadecyl column with a mobile phase of acetonitrile:0.006 M aqueous tetrabutylammonium phosphate, pH 6.5 (20:80). The column effluent is monitored by UV detection at 254 nm. The method is linear, quantitative, and reproducible for a wide variety of formulations. Using this method, the average recovery of 1 from spiked samples was 100%, with a relative standard deviation of less than 2%. The minimal quantifiable level of 1 was approximately 2.8 ng (equivalent to an analytical concentration of 1.5 microgram/mL).